JPH04301598A - Measuring device of fuel rod of fuel assembly - Google Patents

Abstract

PURPOSE:To improve measurement repeatablity of fuel rod gaps of nuclear reactor fuel assemblies and to improvement measuring accuracy and speed. CONSTITUTION:An insertion plate 1 which has a probe at its top end and is inserted among fuel rods, a driving device which puts the insertion plate forwardly and backwardly, and a position detecting mechanism of the probe, which is attached to the driving device, are provided, as well as an ECT coil 7 is provided to the probe, in order to measure fuel rod gaps based on position detection signal and the amperage value of the ECT coil. A penetration hole 9 is provided at the position where the ECT coil is provided on the insertion plate 1, a back side of the ECT coil 7 is exposed from that penetration hole 9 without any shielding, and a posture regulating jig 8 is attached to back and forth, and, above and beneath the ECT coil, as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel rod gap measuring device for measuring the fuel rod gap of a fuel assembly for a nuclear reactor.

0002

[Prior Art] Fuel assemblies used in nuclear power plants generally have a structure in which a large number of fuel rods are arranged side by side in a square matrix, supported by a plurality of support grids at predetermined intervals, and then focused. , are subjected to various periodic inspections to check their soundness.

[0003] Fuel rod gap measurement, which measures the spacing between fuel rods, is one such inspection, and the conventional method for this measurement is to insert a gap sensor using a strain gauge or a clearance gauge between the fuel rods. Measurement methods or methods of measuring on a screen whose dimensions have been calibrated using a television camera image have been adopted.

However, the method using strain gauges has the disadvantage that the strain gauges are easily damaged and lacks stability, and the method of measuring by inserting a feeler gauge is a contact method, which applies force to the fuel rods, making accurate measurement difficult. Great care must be taken to obtain the value.

Furthermore, the comparatively calibrated method of measuring on a television screen is an excellent method as a remote measurement method, but there are problems such as it is difficult to prove and it is difficult to set conditions to obtain a good image. .

[0006] Therefore, the present applicant attempted to improve the above-mentioned drawbacks,
First, an eddy current coil (ECT coil) is used, and it is equipped with an insertion plate that has a probe at the tip and is inserted between the fuel rods, and a drive device that drives the insertion plate so that it can move forward and backward. A position detection mechanism for detecting the position of the fuel rod is provided, and an ECT coil for detecting the distance to the fuel rod by a current value is provided on the probe, and these position detection signals and ECT are provided.
We have proposed a fuel rod gap measuring device configured to measure the fuel rod gap based on the current value of the coil. (Patent Application No. 149526/1999)

[0007]

However, the probe used in the above device, that is, the gap sensor, has an iron core (10) covered with a plastic tube (11) connected to a conductive cable (14) as shown in FIG. Copper wire (1
2), and an ECT coil (7) with a plastic disk (13) attached to one side is attached to the tip of the insertion plate (1), and a magnetic shielding member (15) is attached to the back side of the plastic disk (13). 2 which bulged out in the shape of an embedded circular arc attached to the
This is equipped with a positioning metal fitting (8), and if the coil is directed only to one side like this, the side opposite the coil of the insertion plate will necessarily come into contact with the fuel rod on one side that forms the gap. This is a condition for accurate gap measurement.

[0008] However, as a practical problem, the insertion plate tends to float even though the positioning metal fittings are provided as described above. This is thought to be because the arrangement of the fuel rods is actually uneven when looked at in detail.

Therefore, the present invention further focuses on these points and improves the gap sensor described above to increase the degree of freedom regarding the positional relationship between the insertion plate and the fuel rod, improve the reproducibility of gap measurement, and improve measurement accuracy and measurement. The purpose is to further improve speed.

0010

[Means for Solving the Problems] That is, the features of the present invention to meet the above object include: an insertion plate having a probe at the tip thereof and inserted between fuel rods; The drive device is provided with a position detection mechanism that detects the position of the probe, and the probe is provided with an ECT coil that detects the distance from the fuel rod by a current value, and these position detection signals are provided. In the fuel rod gap measuring device configured to be able to measure the fuel rod gap based on the current value of the ECT coil and the ECT coil of the insertion plate,
A through hole is provided at the coil installation position, and the back side of the ECT coil is exposed from the through hole without shielding, and
This is because posture adjustment jigs are attached to the front, rear, left and right sides of the ECT coil.

[0011]The ECT coil in this specification refers to Eddy Current Testing Coil.
It is called a coil (eddy current coil) and is commercially available.

0012

[Operation] According to the measuring device of the present invention having the above configuration,
First, insert the insertion plate into any row and row of the fuel rods arranged in a square matrix (
The probe at the tip of the insertion plate is moved to the back by a drive device.

At this time, the current flowing through the ECT coil changes more strongly as the fuel rods located in front of the coil are closer due to the characteristics of eddy currents, and by comparing the strength of this current value with the position detection signal, each fuel rod is The distance (interval) in the column (row) direction can be measured. Moreover, in the configuration of the present invention, there is a through hole on the back side of the ECT coil, and the interval between the fuel rods can be measured on both the front and back sides of the ECT coil.

At the same time, as the probe continues to move as described above, the current value alternately shows strong and weak values, and the interval between adjacent strong values is compared with the position detection signal. By doing so, the distance in the row (column) direction of each fuel rod perpendicular to the above direction is measured.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the measuring device of the present invention will be described below with further reference to the accompanying drawings.

FIG. 4 is an explanatory diagram showing a measuring device according to an embodiment of the present invention. In the figure, (1) shows a probe (2) at its tip.
) is integrally provided and inserted between the fuel rods, an insertion plate (3
) is a drive device that drives the insertion plate (1) so as to move forward and backward in the direction of the arrow in the figure, (4) is an intermediate processing device that converts the signal of the probe (2) into a measurement value, and (5) is the drive device (3). ), the position detection mechanism (6) detects the position of the probe (2) provided in the probe (2);
) are shown, respectively.

As shown in FIG. 5, the insertion plate (1) is made of an elongated thin plate, and has a probe (1) integrally formed at its tip.
In 2), an ECT coil (7) is attached, and four attitude adjustment jigs (8) made of elastic leaf springs bulging in an arc shape are provided. In addition, an insertion plate (1
) Near the base is another balance ECT coil (
7') is buried in order to eliminate the influence of temperature, voltage or water pressure on the measured value of the coil (7) of the probe (2), and is always provided as a pair with the coil (7).

The ECT coil (7) is made by winding an iron core (10) covered with a plastic tube (11) with a copper wire (12), as shown in FIG. A plastic disk (13) is attached to the back side, and the copper wire has a diameter of 0.05 to 0.08 mm.
The ECT coil (7) has a diameter of 4 to 8 mm and a thickness of 0.5 to 0.5, excluding the disk (13).
It is as diverse as 0.8mm. Note that if the coil is not circular, but elliptical, for example, with a major axis of about 15 mm and a minor axis of about 10 mm, with the major axis facing the insertion direction, the peak of the signal obtained during insertion will be gentle, making measurement easier. . Moreover, instead of an iron core, an air core made of plastic such as acrylic may be used.

FIGS. 1 to 3 show the attachment part of the ECT coil in the above-mentioned probe, which is the main part of the present invention, and there is a through hole (9) on the back side of the insertion plate (1) where the ECT coil (7) is attached. is provided, and the back side of the ECT coil is exposed through the through hole (9) without being shielded, and posture adjustment jigs (8) are provided on all sides of the front, back, left and right of the ECT coil (7). A leaf spring is attached as a.

In order to measure the gap between these fuel rods not only on one side of the ECT coil but also on both the front and back sides, the positioning metal fittings were provided only on both the left and right sides of the ECT coil (7). This system uses not only the two fuel rods so that the insertion plate enters at right angles to the main fuel rod, but also the two fuel rods before and after the two fuel rods to control the attitude of the insertion plate. This is effective in preventing oblique entry into the gap more reliably and making gap measurement more accurate.

Next, the mode of measurement using the embodiment measuring device having the above configuration will be explained with reference to FIG. 6. First, the insertion plates (1) are arranged according to the number of gaps in the fuel assembly. The fuel rods arranged in a square matrix (N
)...(N) between rows (may be between columns)
, and continue moving the probe (2) at the tip of the insertion plate (1) to the back.

At this time, the attitude adjustment jig (8) comes into contact with the fuel rod (N) facing the front of the ECT coil (7), so that the probe (2) is brought into contact with the fuel rod (N) on the back side. This ensures accuracy in measuring the distance between the fuel rods in the row direction, but at this time, the distance between the fuel rods is also measured on the back side, and the fine irregularities on the fuel rods make it difficult for the probe to be accurate. This improves the reproducibility of gap measurements even when there is no contact with the fuel on the back side.

[0023] Thus, when a current is passed through the ECT coil (7), due to the characteristics of eddy current, the closer the fuel rod (N) located in front of the coil (7) is, the stronger or weaker the current value becomes. The difference (X) of The distance (X') in the column direction of each fuel rod (N) can be measured.

At the same time, since the probe (2) continues to move as described above, the current value alternately shows strong and weak values as shown in FIG. The distance (Y') in the row direction of each fuel rod (N) is calculated by digitizing the value interval (Y) and processing it in the data processing device (6) while comparing it with the position detection signal.
can be measured.

Although the embodiments have been described above, the intermediate processing device and the data processing device do not necessarily need to be provided. Furthermore, because the gap measuring device of the present invention can be used both in the air and underwater due to its structure, it can be applied to spent fuel inspection as well as being effective in measuring the gap of objects other than fuel rods. Of course.

[0026]

As explained above, the fuel rod gap measuring device of the present invention comprises an insertion plate having a probe at the tip and inserted between the fuel rods, and a drive device for driving the insertion plate to move forward and backward. The probe is equipped with a position detection mechanism that detects the position of the drive device and the probe, and an ECT coil that detects the distance to the fuel rod using a current value, and the detection signal of the position detection mechanism is Since the fuel rod gap can be measured based on the strength and weakness of the current in the ECT coil, it can be used to measure gaps from narrow to wide, eliminating the shortcoming of conventional measuring devices, which was the lack of capacity for measuring gaps. Furthermore, since the gap can be measured without contact, the durability of the probe itself is increased, there is no damage to the fuel rods, and the probe can be moved at high speed for quick measurements. It has many excellent effects.

Moreover, the device of the present invention further performs ECT of the insertion plate.
A through hole is provided at the coil position and the fuel rod gap is EC
By measuring on both sides of the T-coil, the condition that the side of the insertion plate opposite to the coil must be in contact with the fuel rod on one side of the gap is relaxed, and the positional relationship between the insertion plate and the fuel rod is relaxed. This has the practical effect of increasing the degree of freedom and improving the reproducibility of gap measurements.In addition, posture adjustment jigs are provided on the front, back, left, and right sides of the ECT coil, making the insertion posture of the insertion plate into the gap more accurate, and improving measurement accuracy. It also has the effect of improving.

[Brief explanation of drawings]

FIG. 1 is a front view showing how an ECT coil, which constitutes a main part of the gap measuring device of the present invention, is attached.

FIG. 2 is a side view showing how the ECT coil is attached.

FIG. 3 is a back view of the ECT coil attachment section.

FIG. 4 is an explanatory diagram showing a gap measuring device according to an embodiment of the present invention.

FIG. 5 is a front view showing the insertion plate of the same embodiment.

FIG. 6 is a plan view showing a measurement state by the apparatus of the embodiment.

FIG. 7 is an explanatory diagram showing an example of signals of the ECT coil of the same embodiment.

FIG. 8 is a partially cutaway perspective view showing the ECT coil embedded state of the measurement device previously proposed by the present applicant.

[Explanation of symbols]

(1) Insertion plate (2) Probe (3) Drive device (4) Intermediate processing equipment (5) Position detection mechanism (6) Data processing device (7) ECT coil (8) Posture adjustment jig (9) Through hole

Claims (1)

[Claims] 1. An insertion plate having a probe at its tip and inserted between the fuel rods, and a drive device for driving the insertion plate to move forward and backward, the drive device having a position for detecting the position of the probe. In addition to providing a detection mechanism, the probe is provided with an ECT coil that detects the distance to the fuel rod by a current value,
In a fuel rod gap measuring device that can measure the fuel rod gap based on these position detection signals and the current value of the ECT coil, a through hole is provided in the insertion plate at the ECT coil installation position, and the back side of the ECT coil is shielded. 1. A fuel rod gap measuring device for a fuel assembly, characterized in that the ECT coil is exposed through the through hole, and attitude adjustment jigs are attached to each of the front, rear, left and right sides of the ECT coil.